Pseudoautosomal Inheritance

Abstract

Traits encoded by genes on the X‐ and Y‐chromosomes are generally inherited in a specific manner, referred to as sex‐linked.
Females receive alleles from their parent's X‐chromosomes, whereas males receive X‐encoded genes from their mother and Y‐encoded
genes from their father. However, a small subset of genes on the X‐ and Y‐chromosomes exhibit a pattern of inheritance that
is not sex‐linked. That is, genes on the Y‐chromosome are sometimes passed to daughters, and genes on the X‐chromosome are
sometimes passed from fathers to their sons. This is possible because the X‐ and Y‐chromosomes share regions of sequence identity,
and these regions undergo recombination during male meiosis. Therefore sequences can be transferred from the X to the Y, and
vice versa. The resulting transmission pattern resembles that which is seen for sequences on autosomes, and is referred to
as pseudoautosomal inheritance.

Key concepts:

The X‐ and Y‐chromosomes contain regions of sequence identity at the ends of their respective short and long arms.

Recombination takes place in male meiosis between the X and Y within these regions of DNA sequence identity.

Traditional patterns of sex‐linked inheritance are sometimes not observed for alleles in these regions of X–Y sequence identity.

The pattern of inheritance observed for alleles in the X–Y identical regions is referred to as pseudoautosomal inheritance,
because it resembles the pattern seen for alleles located on autosomes. The areas of sequence identity on the X and Y are
thus referred to as the pseudoautosomal regions.

The likelihood of observing pseudoautosomal inheritance for a given allele depends on its location within the pseudoautosomal
region: the more distal a locus is, the more likely it will demonstrate pseudoautosomal inheritance.

Keywords: sex chromosomes; pseudoautosomal; recombination

Figure 1.

Pseudoautosomal inheritance of X and Y alleles. The lightly shaded areas represent the identical sequences on the X and Y
short arms that comprise the pseudoautosomal region. It is within this region that recombination takes place between the X
and Y. No recombination occurs between X‐ and Y‐specific sequences, represented by solid green and blue bars, respectively.
The A/a alleles demonstrate pseudoautosomal inheritance, whereas the B/b alleles show sex‐linked inheritance.

Figure 2.

Pseudoautosomal inheritance of XE7 alleles. The figure shows restriction fragment length polymorphisms (RFLPs) at the pseudoautosomal XE7 locus in a three‐generation family. Individuals III‐4 and III‐10 exhibit pseudoautosomal inheritance as a result of exchange
of X and Y alleles in the father (II‐1).
Reproduced with permission from Ellison et al..